Exam 2: Alginate

Question 1

exact time of working time is ______

Answer 1

hard to determine clinically

Question 2

working time begins with the

___ and ends just __________ of the impression material develops

Answer 2

start of mixing, before elastic properties

Question 3

definitions of the working time and setting time show that…(2)

Answer 3

1. working time begins at start of mixing and ends just before elastic properties
2. b/t working time and setting time the material continues to harden until no
   more changes in the mechanical properties occur.

Question 4

high viscosity is a….

Answer 4

thick liquid

Question 5

low viscosity is a…

Answer 5

thin liquid

Question 6

viscosity is a ______

Answer 6

mechanical property

Question 7

viscosity: a measure of its

resistance to ______ by ____ stress or ____ stress

Answer 7

gradual deformation, shear, tensile

Question 8

viscosity depends on…

Answer 8

• composition
• rate of deformation (shearing)
• temperature

Question 9

the higher the molecular weight of a polymer, the _____ the viscosity

Answer 9

higher

Question 10

the higher the filler content, which does not deform, the ____ the viscosity

Answer 10

higher

Question 11

where a material is placed directly into the mouth, where it sets

Answer 11

direct restoration

Question 12

examples of direct restorations

Answer 12

amalgam, resin composites

Question 13

examples of indirect restorations

Answer 13

dentures, ceramics

Question 14

where a restoration or prosthesis is prepared in a laboratory

Answer 14

indirect restoration

Question 15

what does Combe’s law state?

Answer 15

restoration/appliance fabricated in the
lab cannot be more accurate than the
impression from which a working cast is
prepared

Question 16

stages of impression taking

Answer 16

1. insertion
2. setting
3. removal
4. cooling to room temp
5. disinfection
6. storage
7. compatibility with gypsum

Question 17

alginate is…

Answer 17

an irreversible hydrocolloid

Question 18

working time ___ with increase temperatures

Answer 18

decreases

Question 19

when the impression material is removed from the mouth, it is in _______

Answer 19

an elastic state

Question 20

general requirements of impression material

Answer 20

B = nontoxic/nonirritating
I = good wetting
C = long shelf life
M = good resistance to tearing
E = acceptable odor/taste
P = appropriate working/setting time

Question 21

notes on dimensional stability/accuracy

Answer 21

• impressions are hydrophilic
• working time/viscosity are important
• once removed, enough elasticity for removal & enough strength to resist tearing
• disinfection shouldn’t change impression

Question 22

two types of elastic materials

Answer 22

elastomers, hydrocolloids

Question 23

_____ materials are rigid when set, and will deform or fracture when displaced from undercuts

Answer 23

non-elastic

Question 24

_______ are aqueous materials, with poor strength and stability

Answer 24

hydrocolloids

Question 25

_______ are non-aqueous synthetic rubbers, which are more stable and stronger than hydrocolloids

Answer 25

elastomers

Question 26

hydrocolloid dispersion medium

Answer 26

water

Question 27

``` a suspension of finely divided particles (dispersed), suspended uniformly in a dispersion medium (dispersant) from which the particles do not settle out rapidly/cannot readily be filtered ```

Answer 27

colloid

Question 28

can a colloid be readily filtered?

Answer 28

no

Question 29

a colloidal dispersion of very small | particles in a continuous liquid medium

Answer 29

sol

Question 30

a suspension where the dispersed phase | forms agglomerates in the form of chains or fibrils

Answer 30

gel

Question 31

sol is a ___ while gel is a _____

Answer 31

fluid; elastic solid

Question 32

loss of fluids by the material

Answer 32

syneresis

Question 33

uptake of fluids by the material

Answer 33

imbibition

Question 34

syneresis results in ____

Answer 34

shrinkage

Question 35

imbibition results in ____

Answer 35

expansion

Question 36

main components in alginate

Answer 36

water, powder

Question 37

what is the powder in alginate?

Answer 37

- soluble salt of alginic acid - Ca salt - trisodium phosphate - filler

Question 38

what is the alginic acid in alginate?

Answer 38

sodium alginate

Question 39

sequential reactions of alginate

Answer 39

- formation of calcium phosphate (1. retarder) | - formation of calcium alginate (gel) (2. setting)

Question 40

marks of good alginates

Answer 40

- well defined working time - elastic - records fine detail - comparatively inexpensive

Question 41

marks of poor alginates

Answer 41

- dimensionally unstable | - tears easily

Question 42

trisodium phosphate acts as a....

Answer 42

retarder

Question 43

purpose of calcium salt in alginate

Answer 43

provides reaction for sol to gel (setting mechanism)

Question 44

prevent tearing by removing impression with a...

Answer 44

sharp movement

Question 45

best use for study casts...

Answer 45

prosthodontics/orthodontic

Question 46

study casts are insufficient/unstable for...

Answer 46

bridges, inlays, crowns